Electron transfer. 137. Formal potentials involving indium(II)

Aqueous solutions of indium(III) undergo 1e⁻ reductions by Sm(II) (E⁰-1.55 V) and by Yb(II) (−1.05 V), but not by U(III) (−0.52 V). The facile and irreversible reduction, by In⁺ _aq, of Ru(NH₃)₆ ³⁺ (E⁰+0.067 V) at reagent concentrations near 10⁻³ M implies a potential more negative than −0.23 V for In(II,I) and, in conjunction with the known value of −0.44 V for In(III,I), a complementary potential less negative than −0.65 V for In(III,II). These observations, taken together, support le⁻ indium potentials E_II,I ^o−0.2 V and E_III,II ⁰−0.6 V.     

Another Approach to the Modified Zhuravlev Equation on the Basis of the Oxidation of V2O4 and V6O13

It has been found that the modified Zhuravlev equation, [(1−α)^−1/3−1]²=ktⁿ, which describes the kinetics of oxidation of V₂O₄ and V₆O₁₃ in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol⁻¹ for V₂O₄ and 188–201 kJ mol⁻¹ for V₆O₁₃ in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydrolysis of titanium sulphate compounds

The influence of TiOSO₄ and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO₄ in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³) and 92 % (300 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³). The same relation was obtained when changing the concentration of free H₂SO₄ in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³) and 96 % (136 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Electron transfer. 138. Potentials involving chelated chromium(V)

The bis(chelated) complex of Cr^V(0) derived from the dianion (L^{2 −}) of 2-ethyl-2-hydroxybutanoic acid is readily reduced to a bis(chelate of Cr^III, featuring the monoanion (LH⁻) [Cr ^V(0)(L²⁻)₂]⁻+4H⁺+H₂O+2e⁻→[Cr^III(OH₂)₂(LH⁻ ₂]⁺ of this acid. Potentials estimated by Ghosh in 1993 for this 2e⁻ change, E⁰ (pH 0) 1.32 V, E^eff (pH 3.3) 0.93 V, are in accord with the nearly irreversible reductions of the Cr(V) species (in 1∶1 ligand buffer) by Fe²⁺, V0²⁺, IrCl₆ ^{3 −} and I⁻, whereas lower values reported by Bose in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.45 V, are potentiometrically inconsistent with these conversions. A similar discrepancy is noted for potentials for Cr(V,IV) estimated in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.46 V, which, wholly contrary to observation, predict that the reductions of excess Cr(V) to CR(IV) by Fe²⁺, V0²⁺, and I⁻ are thermodynamically disfavored.     

Synthesis of N'-substituted amidines through the cleavage an oxadiazolone heterocycle by weakly basic nucleophiles. Effect of the nature of the nucleophile and of the nucleophile/substrate molar ratio

The reaction of 1-ethoxycarbonylmethyl-5,5,7,7-tetramethyl-2-oxo-tetrahydroimidazo[1,5-b]oxadiazol-6-oxyl with the weakly basic nucleophiles NaN₃, NaCN, KF, KBr, KCl and NaNO₂ has been studied. It was shown for the first time that, as in the case of NaOH and MeONa, the reaction occurs with opening of the oxadiazolone ring to form exo-N-substituted amidines. It was shown that the weakly basic nucleophiles readily react with substrates which contain a substituent sensitive to attack by such nucleophiles as NaOH or MeONa. The effect of the nature of the nucleophiles on the reaction course for opening of the oxadiazolone ring was also studied. It was found that the reactivity of the nucleophiles in DMSO changes in the series F⁻ > CN⁻ > N₃^– >NO₂⁻ > Cl⁻ > Br⁻ and qualitatively correlates with their basicities in this solvent. Examination of the effect of the ratio of the reagents on the degree of conversion of the starting oxadiazolone has shown that a quantity of nucleophiles less than one equivalent also allowed the cleavage reaction of the oxadiazolone heterocycle to go to completion through just increasing the reaction time. The experimental data obtained lends support to the proposed reaction scheme. Dedicated to Academician B. A. Trofimov in his 70^th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 71–78, January, 2009.     

Simultaneous ion chromatographic determination of selenium and metal ions in waters at trace level

Summary An ion-chromatographic procedure is described for the determination of selenium (VI) at μg L⁻¹ level in the presence of anions and heavy metal ions. Maximum permissible concentrations and effects from each interfering substance were investigated for the Se concentration range 12.5–1,000 μg L⁻¹. The method, optimized for the detection of SeO ₄ ²⁻ , gives results suitable for speciation analysis. Total selenium can be determined after complete conversion to selenate ion by oxidation with KMnO₄. The detection limit of selenium is 4.8 μg L⁻¹ (0.96 ng for 200 μL sample). Paper presented at the 41st Pittsburgh Conference, New York, March 5–9, 1990.     

Oxidation of Fe(III) to Fe(VI) by ozone in alkaline solutions

The action of ozone on a suspension of Fe(III) hydroxide in alkaline solutions was studied by the spectrophotometric method. A partial conversion of Fe(III) to Fe(VI) is observed at Fe(III) concentrations exceeding 2 mmol l⁻¹. The tenfold increase of the initial Fe(III) concentration raises the Fe(VI) yield by a factor of 2–3. The mechanism of the process includes the decomposition of ozone with the formation of ozonide ions, which oxidize Fe(III) up to Fe(IV), Fe(V), and Fe(VI) in parallel with their conversion to O₂⁻ and HO₂⁻. Fe(VIII) is not formed.     

Neutral thallium clusters in aqueous solutions. Pulse radiolysis study

The formation of neutral Tl₂ (λ_max = 390 nm) and Tl₄ (λ_max = 360 nm) clusters in dilute aqueous solutions of Tl₂SO₄ containing formate ions was found by pulse radiolysis. The rate constants for the recombination of Tl⁰ atoms and Tl₂ clusters are equal to 1.5·10¹⁰ L mol⁻¹ s⁻¹ and 1.0·10¹⁰Lmol⁻¹ s⁻¹ (±30%), respectively, and the extinction coefficient of Tl₂ at 390 nm is −6.0·10³ L mol⁻¹ cm⁻¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2367–2369, December, 1999.     

Oxidation of 1,3,7-trimethylxanthine by hypochlorite ion

The kinetics of the oxidative conversion of 1,3,7-trimethylxanthine upon treatment with hypochlorite ions (OCl⁻) in aqueous medium at 283–298 K and pH 8.2 was studied. The reaction order with respect to each component was determined and proved to be 1. It was established that the temperature dependence of the reaction rate follows the Arrhenius equation. The activation parameters of the reaction were measured: E _a = 33.58 kJ/mol, ΔH ^≠ = 31.12 kJ/mol, ΔS ^≠ = −170.02 J/(K mol), ΔG ^≠ = 81.45 kJ/mol. The stoichiometry of the reaction was studied, and the chemistry of the oxidative conversion of caffeine treated with OCl⁻ is discussed.     

Low-temperature activation of nitrogen oxide on Cu-ZSM-5 catalysts

The adsorption and activation of NO molecules on Cu-ZSM-5 catalysts with different Cu/Al and Si/Al ratios (from 0.05 to 1.4 and from 17 to 45, respectively) subjected to different pretreatment was studied by ultraviolet-visible diffuse reflectance (UV-Vis DR). It was found that the amount of chemisorbed NO and the catalyst activity in NO decomposition increased with an increase in the Cu/Al ratio to 0.35–0.40. The intensity of absorption bands at 18400 and 25600 cm⁻¹ in the UV-Vis DR spectra increased symbatically. It was hypothesized that the adsorption of NO occurs at Cu⁺ ions localized in chain copper oxide structures with the formation of mono- and dinitrosyl Cu(I) complexes, and this process is accompanied by the Cu²⁺...Cu⁺ intervalence transfer band in the region of 18400 cm⁻¹. The low-temperature activation of NO occurs through the conversion of the dinitrosyl Cu(I) complex into the π-radical anion (N₂O₂)⁻ stabilized at the Cu²⁺ ion of the chain structure, [Cu²⁺-cis-(N₂O₂)⁻], by electron transfer from the Cu⁺ ion to the cis dimer (NO)₂. This complex corresponds to the L → M charge transfer band in the region of 25600 cm⁻¹. The subsequent destruction of the complex [Cu²⁺-cis-(N₂O₂)⁻] at temperatures of 150–300°C leads to the release of N₂O and the formation of the complex [Cu²⁺O⁻], which further participates in the formation of the nitrite-nitrate complexes [Cu²⁺(NO₂)⁻], [Cu²⁺(NO)(NO₂)⁻], and [Cu²⁺(NO₃)⁻] and NO decomposition products.     

Studies on phosphatidylserine by tandem quadrupole and multiple stage quadrupole ion-trap mass spectrometry with electrospray ionization: Structural characterization and the fragmentation processes

Low-energy CAD product-ion spectra of various molecular species of phosphatidylserine (PS) in the forms of [M−H]⁻ and [M−2H+Alk]⁻ in the negative-ion mode, as well as in the forms of [M+H]⁺, [M+Alk]⁺, [M−H+2Alk]⁺, and [M−2H+3Alk]⁺ (where Alk=Li, Na) in the positive-ion mode contain rich fragment ions that are applicable for structural determination. Following CAD, the [M−H]⁻ ion of PS undergoes dissociation to eliminate the serine moiety (loss of C₃H₅NO₂) to give a [M−H−87]⁻ ion, which equals to the [M−H]⁻ ion of a phoshatidic acid (PA) and give rise to a MS³-spectrum that is identical to the MS²-spectrum of PA. The major fragmentation process for the [M−2H+Alk]⁻ ion of PS arises from primary loss of 87 to give rise to a [M−2H+Alk−87]⁻ ion, followed by loss of fatty acid substituents as acids (R_xCO₂H, x=1,2) or as alkali salts (e. g., R_xCO₂Li, x=1,2). These fragmentations result in a greater abundance of [M−2H+Alk−87−R₂CO₂H]⁻ than [M−2H+Alk−87−R₁CO₂H]⁻ and a greater abundance of [M−2H+Alk−87−R₂CO₂Li]⁻ than [M−2H+Alk−87−R₁CO₂Li]⁻; while further dissociation of the [M−2H+Alk−87−R_{2(or 1)}CO₂Li]⁻ ions gives a preferential formation of the carboxylate anion at sn-1 (R₁CO₂⁻) over that at sn-2 (R₂CO₂⁻). Other major fragmentation process arises from differential loss of the fatty acid substituents as ketenes (loss of R_x′CH=CO, x=1,2). This results in a more prominent [M−2H+Alk−R₂′CH=CO]⁻ ion than [M−2H+Alk−R₁′CH=CO]⁻ ion. Ions informative for structural characterization of PS are of low abundance in the MS²-spectra of both the [M+H]⁺ and the [M+Alk]⁺ ions, but are abundant in the MS³-spectra. The MS²-spectrum of the [M+Alk]⁺ ion contains a unique ion corresponding to internal loss of a phosphate group probably via the fragmentation processes involving rearrangement steps. The [M−H+2Alk]⁺ ion of PS yields a major [M−H+2Alk−87]⁺ ion, which is equivalent to an alkali adduct ion of a monoalkali salt of PA and gives rise to a greater abundance of [M−H+2Alk−87−R₁CO₂H]⁺ than [M−H+2Alk−87−R₂CO₂H]⁺. Similarly, the [M−2H+3Alk]⁺ ion of PS also yields a prominent [M−2H+3Alk−87]⁺ ion, which undergoes consecutive dissociation processes that involve differential losses of the two fatty acyl substituents. Because all of the above tandem mass spectra contain several sets of ion pairs involving differential losses of the fatty acid substituents as ketenes or as free fatty acids, the identities of the fatty acyl substituents and their positions on the glycerol backbone can be easily assigned by the drastic differences in the abundances of the ions in each pair.     

Methane conversion to C2 hydrocarbons in solid electrolyte membrane reactors

Solid electrolyte membrane reactors (SEMRs) have been used to both study and influence catalytic reaction rates. Methane coupling is the reaction most thoroughly and intensively studied in these membrane reactors. In the last 20 years, oxygen ion (O²⁻), proton (H⁺) and mixed (O²⁻-e⁻, H⁺-e⁻) conducting membranes have been tested in order to maximize the conversion of methane to C₂ compounds. The present review contains the fundamental operating principles of the various SEMR types and their applications in this reaction. The difficulties that should be overcome in order to promote this SEMR process to an industrial scale are discussed.     

Ligand Exchange Processes on Solvated Lithium Cations. II. Complexation by Cryptands in γ-Butyrolactone as Solvent

Kinetic studies on Li⁺ exchange between the cryptands C222 and C221, and γ-butyrolactone as solvent were performed as a function of ligand-to-metal ratio, temperature and pressure using ⁷Li NMR. The thermal rate and activation parameters are: C222: k ₂₉₈ = (3.3 ± 0.8)×10⁴ M⁻¹ s⁻¹, ΔH ^# = 35 ± 1 kJ mol⁻¹ and ΔS ^# = −41 ± 3 J K⁻¹ mol⁻¹; C221: k ₂₉₈ = 105 ± 32 M⁻¹ s⁻¹, ΔH ^# = 48 ± 1 kJ mol⁻¹ and ΔS ^# = −45 ± 2 J K⁻¹ mol⁻¹. Temperature and pressure dependence measurements were performed in the presence of an excess of Li⁺. The influence of pressure on the exchange rate is insignificant for both ligands, such that the value of activation volume is around zero within the experimental error limits. The activation parameters obtained in this study indicate that the exchange of Li⁺ between solvated and chelated Li⁺ ions follows an associative interchange mechanism. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . For Part I see: R. Puchta, M. Galle, N.J.R. van Hommes, E. Pasgreta and R. van Eldik: Inorg. Chem. 43, 8227 (2004).     

Further studies on polyhalide formation in polar solvents using the positron annihilation lifetime spectroscopy

The rate constants for the reactions of positronium with I ₃ ⁻ , Br⁻, and I⁻ in dimethylsulphoxide (DMSO) and for I ₃ ⁻ in water have been determined, and the orthopositronium lifetime variations have been used for studying polyhalide formation in the (I₂+Br⁻)/DMSO system. It is found that the formation of more than one polyhalide is needed to account for the data. On basis of this new evidence, previous results in methanol and in DMSO are re-examined. Besides the primary I₂X⁻ (X⁻: halide), I₂X ₂ ²⁻ complexes have to be invoked. Trial absorption measurements confirm the presence of solvolysis equilibria for I₂ in DMSO. Taking these facts into account, much higher, albeit poorly defined, values than previously reported are found for the I₂X⁻ formation constants. The reliable K_c values deduced are 28M⁻¹, 0.57M⁻¹ and 2.5M⁻¹ respectively for I₂Cl⁻, I₂Cl ₂ ² and I₂Br ₂ ²⁻ in methanol, and 1.4M⁻¹ and 0.8M⁻¹, respectively for I₂Cl ₂ ²⁻ and I₂Br ₂ ²⁻ in DMSO.     

Synthesis and anion recognition of neutral receptors based on multiamide calix[4]arene

Two multiamide calix[4]arenes (5, 6) were synthesized and characterized by NMR, MS and elemental analysis. The binding properties of receptors with some anions (π-O₂NPhOPO₃²⁻, π-O₂NPhO⁻, H₂PO₄⁻, Ac⁻, Cl⁻, Br⁻ and I⁻) were studied by UV-Vis spectra. The results indicate that the tetraamide calix[4]arenes (5, 6) have a good selectivity to the anions containing aromatic ring (π-O₂NPhOPO₃ ²⁻, π-O₂NPhO⁻). The 1 : 1 complexes between host and guest were formed through multiple hydrogen bonding and π-π interactions. The hosts 5 and 6 also show a definite binding ability for the anions (H₂PO₄⁻, Ac⁻, Cl⁻) that have no ultraviolet absorption, which provides a simple method of spectrum detection for these anions.     

Nucleophilic Substitution Reactions at Planar Tetra-coordinate Bis-cationic-platinum(II) Complexes. Kinetics of Displacement of Pyridine from {Pt[2,6-bis(methylthiomethyl)pyridine](py)}2+, {Pt[bis(2-pyridylmethyl)amine] (py)}2+ and {Pt[bis(2-(pyridylmethyl)sulphide](py)}2+ Cations

The kinetics of nucleophilic substitution of pyridine in bis-cationic [Pt(L)(py)]²⁺ complexes (L=SNS, NNN, NSN) [SNS=bis(methylthiomethyl)pyridine, NNN=bis(2-pyridylmethyl)amine, NSN=bis(2-pyridylmethyl)sulphide] by a series of nucleophiles (Cl⁻, Br⁻, I⁻, N₃⁻, (C₂H₅)₂S, NH₃, thiourea (tu), NO₂⁻, C₅H¹0NH, SeCN⁻, SCN⁻, CN⁻ when L=SNS; Cl⁻, Br⁻, I⁻, N₃⁻, (C₂H₅)₂S, SCN⁻, NH₃, NO₂⁻ when L=NNN; Br⁻, N₃⁻, NO₂⁻, NH₃, C₅H₁₀NH when L=NSN) have been measured in MeOH at 25 °C, μ =0.1 mol dm⁻³ (LiClO₄ or LiCF₃SO₃). The logarithms of the second-order rate constants calculated at μ=0, log k° ₂, do not follow the dependence upon the n° _Pt scale. In particular, the reactivity of the biphilic reagents tu, SeCN⁻, SCN⁻ and, to a lesser extent, NO⁻ ₂, towards these doubly charged substrates is largely lower than expected on the basis of the n° _Ptscale. There are good linear relationships between logk° ₂ for the bis-cationic substrate [Pt(SNS)(py)]²⁺, chosen as the standard, and log k° ₂ for the same reactions with [Pt(NNN)(py)]²⁺, [Pt(NSN)(py)]²⁺ and other double charged complexes previously studied. A new wide nucleophilicity scale based on [Pt(SNS)(py)]²⁺, that is appropriate to all the bis-cationic substrates, is here proposed     

DDTC-Na-based colorimetric chemosensor for the sensing of cyanide in water

Sodium diethyldithiocarbamate (DDTC-Na) was demonstrated to be a new colorimetric cyanide chemosensor by utilizing an indirect trick. First, some copper ions were added to the colorless aqueous solution of DDTC-Na. Then, the resultant brown solution was studied upon the addition of different anions, including Cl⁻, I⁻, IO₃⁻, SO₄²⁻, NO₂⁻, Br⁻, H₂PO₄⁻, F⁻, SCN⁻, HSO₄⁻, ClO₄⁻ and CN⁻. It was observed by naked eyes that the brown solution changed to colorless immediately after the addition of the trace cyanide, but there were no changes towards other anions, making DDTC-Na a good selective cyanide chemosensor in pure water. Supported by the National Natural Science Foundation of China (Grant Nos. 20674059 & 20402011)     

TOF-SIMS imaging of halide/thiocyanate anions and hydrogen sulfide in mouse kidney sections using silver-deposited plates

In vivo imaging of reactive small molecule metabolites with high spatial resolution and specificity could give clues to understanding pathophysiology of various diseases. We herein applied time of flight-secondary ion mass spectrometry (TOF-SIMS) to newly developed silver-deposited plates that were stamped on mouse tissues, and succeeded in visualization of halide (Cl⁻, Br⁻, and I⁻) and pseudohalide thiocyanate (SCN⁻) anions, a class of substrates for neutrophils/eosinophil peroxidases to produce hypohalous acids (HOX/OX⁻ mixture; X: (pseudo)halides), as well as hydrogen sulfide (H₂S). Forty-micrometer frozen mouse kidney sections on cover glasses were attached to 37 °C preheated silver-deposited plates and incubated at −10 °C for 1 h. After sputter cleaning to remove surface contaminants, the plates were analyzed by TOF-SIMS to identify distribution of Br⁻, AgBr₂⁻, I⁻, AgI₂⁻, SCN⁻, as well as S²⁻ and AgS⁻ as products of tissue-derived H₂S. Br⁻, AgBr₂⁻, I⁻, and SCN⁻ anions were mainly distributed in core regions including the inner medulla and inner stripe of the outer medulla (except for I⁻), rather than outer regions such as the cortex and outer stripe of the outer medulla. AgI₂⁻ anion was spread over the whole kidney, although its levels were relatively low. In contrast, S²⁻ and AgS⁻ anions were mainly present in the outer regions. To our knowledge, this is the first imaging study to reveal the distribution of (pseudo)halides and H₂S in animal tissue sections.     

Photofixation of carbon dioxide in semiconductor particulate and microbial systems

Photocatalytic reduction of CO₂ to HCOOH and HCHO was carried out in a Pt/CdS/RuO₂ semiconductor particulate system using [Ru^III(EDTA-H)H₂O] complex as catalyst. Upon illumination at 505 nm (band gap energy of CdS), the system produced HCOOH and HCHO at rates equal to 3.05 × l0⁻² Mh⁻¹ and 2.0 × 10⁻² M h⁻¹, respectively. Trace amounts of CH₂OH, CH₄ and CO were also detected in the reaction vessel. Photobiological conversion of CO₂ to formic acid was achieved by usingHalobacterium halobium MMT₂₂ in aqueous solution at a rate equal to 0.45 M h⁻¹. A one-and-half-fold increase in the rate of formation of formic acid was observed when the photobiological reduction of CO₂ was performed in the presence of L-ascorbic acid as electron-donating agent and [Ru^III(bipy)₃]²⁺ as photosensitizer.